The present invention relates to a reproducing piano and more particularly to a reproducing piano that sorts the notes to be reproduced according to intensity and subsequently reproduces the notes at or near the original recorded intensity.
It is known to record performances of a piano on magnetic tape, for example, and reproduce the performance by playing the tape and causing the keys to be actuated mechanically. During the record mode, the piano is played by a musician, and sensors detect the timing and velocity with which the keys are depressed or the hammers are moved, and this information is stored digitally in a permanent memory, such as a magnetic tape. During playback, the digital information is retrieved from the tape and converted to control signals that energize actuators to play the keys in the same pattern and with the same dynamics as during the original performance.
In U.S. Pat. No. 4,307,648, which patent is incorporated herein by reference, there is disclosed a method and apparatus for measuring the dynamics of a piano performance wherein a shutter is provided for each hammer shank of the piano, as well as a separate optical switch assembly and counter that is responsive to the trigger signals produced as the shutter eclipses the light beam, the counter is responsive to an initiating signal from the optical switch assembly to start the counter and to an end of count signal from the optical switch to terminate the count, the total count defining the count increment. The total count registered comprises a digital signal constituting an inverse function of the near terminal hammer velocity, that is, the velocity of the hammer just before it strikes the string. Digital information corresponding to the count is stored on magnetic tape for recall during playback and reproduction of the original performance.
A microprocessor retrieves the data from the magnetic tape and produces a digital drive value corresponding to the particular key velocity required. A digital-to-analog converter converts the digital drive value to an analog voltage, and a feedback servomechanism comprising a plurality of operational amplifiers and a sense coil is connected to a solenoid and energizes the solenoid with a current that produces a constant velocity. The velocity is maintained constant by means of the auxiliary sense coil within which a permanent magnet connected to the solenoid plunger moves; the coil is connected to the input of the first operational amplifier. This circuit arrangement causes the solenoid to operate as a linear motor with constant velocity, thereby ensuring that transit times and key velocity can be maintained within very close tolerances so that the playback performance is an accurate reproduction of the original performance.
This linear key velocity technique and system for playback of musical performances yields an extremely accurate reproduction; however, at a considerable expense. Each of the 88 keys has its own operational amplifier servomechanism comprising: a digital-to-analog converter, three operational amplifiers and an input from a triangular wave generator as shown in FIG. 2 of U.S. Pat. No. 4,593,592, which is hereby incorporated by reference. For all the keys on a piano, then, this extremely accurate reproduction system requires a total of 264 operational amplifiers and 88 digital-to-analog converters in order to drive the 88 solenoid actuators for the 88 key analog to digital converters.
Considering that the maximum number of notes that can be played by a performer is twelve, most of the 88 individual circuits of the key velocity reproduction system are not being used at any one time.
Accordingly, it is desirable to provide a reproducing piano which multiplexes a number of digital-to-analog converters and a number of driving circuits in order to reduce the expense and the complexity of 88 individual circuits.
A type of multiplexing reproducing piano is known from U.S. Pat. No. 4,135,428. This known reproducing piano has two multiplexed pulse-width modulators for driving all of the solenoid actuators, one of which is assigned to the bass half of the keyboard and the other of which is assigned to the treble half of the keyboard. With this arrangement, notes that are played on the same half of the keyboard and substantially concurrently, such as the notes of a chord, are all reproduced at the same intensity, because all the treble solenoid actuators are driven from one pulse-width modulator drive signal output and all the bass solenoid actuators are driven from the other pulse-width-modulator drive signal output. This system then reproduces two concurrently struck notes on the same half of the keyboard with equal intensity, and similarly it reproduces all of the notes in most chords with equal intensity. When all of the notes are played with equal intensity, the reproduction has a certain "mechanical" quality to it, which is both noticeable and objectionable. Some of this "mechanical" quality may be overcome by time shifting the notes using known techniques, but this requires an extensive amount of processing of the recorded performance in order to produce a recording tape for playback.
Accordingly, it is desirable to provide a reproducing piano which has a number of possible solenoid actuator drive signals to which the keys may be multiplexed, thereby reproducing multiple sound intensities for notes which are struck substantially concurrently. Moreover, it is desirable to provide a "non-mechanical"-sounding reproducing piano which does not require extensive monetary investments in the editing and processing required between the recording stage and the reproduction stage of the musical performance.